JPH0353184A - Distance measuring equipment - Google Patents

Abstract

PURPOSE:To prevent the dependency of the distance measuring capability upon the temperature by changing a ratio of the drop voltage from the breakdown voltage of an avalanche photo diode (APD) in accordance with the ambient temperature. CONSTITUTION:Capacitors 18 and 19 whose temperature capacity change characteristics are positive and 0 respectively and a first FET 12 perform the voltage drop operation. When capacity values of capacitors 18 and 19 are C1(T) and C2(T is the ambient temperature) respectively, a ratio of the voltage applied to the capacitor whose temperature capacity change characteristic is 0 is C2 :C1(T). Consequently, the charging voltage is dropped by the voltage applied to the capacitor, whose temperature characteristic is positive, at the time of earthing the capacitor 19 by an FET or the like, and its drop rate Z has a higher value at a lower temperature as shown by C1(T1)<C1(T2) for C2/C1(T)+ C2(T1<T2). After an APD 15 causes a breakdown phenomenon, the timing signal of a breakdown detecting circuit 17 is switched from the low level to the high level, and the FET 12 is turned on, and the capacitor 18 is earthed, and the voltage dropped by the drop rate Z is applied to the APD 15.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is a distance measuring device using a laser beam. ! ! l
! ! The receiving APD (Avalanche P
This invention relates to an improvement in the bias application method for photodiodes.

[Conventional technology]

Figure 10 is a block diagram showing a conventional distance measuring device equipped with a photodetector. In the figure (1) is a laser oscillator. +21 is the transmission optical system. (3) is the receiving optical system. C4) is for example PD
(Photo Diode) etc. is used to detect fl-photodetection a, (photodetection unit composed of 5rFi APD.
/61Fi high voltage circuit, 17) is a counting circuit. C8) is a power supply.

In this distance measuring device, a pulsed laser beam is emitted from a laser oscillator (1), and the beam spread is adjusted by the transmission optical system (2), and the laser beam is irradiated toward the target. A part of the signal is input to the photodetector (4), which generates a pulsed electrical signal indicating the timing at which the laser beam is emitted (hereinafter, this signal will be referred to as the start pulse signal).
).

The laser beam reflected from the target is focused by the receiving optical system +31. The photodetector +51 generates a pulsed electrical signal (
(This signal will be referred to as a stop pulse signal hereinafter) is subjected to K conversion. High voltage circuit (81 is the above-mentioned party detection section (51APD)
Create an appropriate bias condition by applying a high voltage to the and. It is used to supply high voltage current for laser beam generation to the laser oscillator +1). ! The power source {8} supplies electrical energy to electronic circuits such as the high voltage circuit (6}, the photodetector (4), the photodetector (5), and the counting circuit (7).

In this way, Rade oscillation a(r), transmission optical system C2》. Receiving optical system (3), photodetector C4]. Photodetector (5). A laser beam for distance measurement is generated in the high voltage circuit (6) and the power source (8), and. Start pulse signal indicating the time when the laser beam was emitted. By the stop pulse signal (1
>>The distance R to the target can be determined by calculating the formula.

CT R=-2 ・・・・・・・・・・・・{1} R: Distance at target 1 (FF!) C: Speed of light (3 x 1 G” m/sec) T: Start pulse signal The time interval (see) between the stop pulse signal and the laser beam reflected from the target is weak.The photodetector (5) that receives the laser beam and generates the stop pulse signal generally has a light multiplication function. The APD is designed to make the most of the APD function by applying a bias voltage just before the APD causes the plaque town phenomenon to the APD.Figure 1) shows this photodetector (5) ). In the figure, 9》 is a current limiting resistor,
aI1aJ) are the 10th and 2nd capacitors, a
zasFi are the 10th and 2nd FETs, and α4 is a diode. α3 PAPD, (+1 is an amplifier. llIt+ is a breakdown detection circuit, and the current limiting resistor (9) and the breakdown detection circuit (7) are connected to the high voltage circuit (6) and the counting circuit (71). In this detection section (5), the APDα has the role of converting the laser beam reflected from the target into a pulsed electrical signal.
The amplifier as amplifies this pulse-like electrical signal to generate a stop pulse signal, and also serves to amplify micronoise generated when the APDu causes a breakdown phenomenon to an appropriate value. Breakdown detection circuit ●The power is the micro noise mentioned above. It serves to send only the stop pulse signal among the stop pulse signals to the counting circuit (71), and also generates a timing signal for bias-controlling the APDLi using the laser firing command signal and the amplified micronoise. Depending on the timing signal, the 10th second FETa3, @3 is normally turned on and turned off just before emitting the laser.Then, the above AP
When D a3 causes a breakdown phenomenon, it operates in such a way that it turns on again. During ON operation, the current limiting resistor (9) and the second capacitor ALL are electrically grounded. Here, the tenth second capacitor a●.
aO is the capacitor whose capacitance value is set to a ratio of 1:(k-1) (k#i proportionality constant), and the high voltage of the high voltage circuit f61 is applied through the current limiting resistor (91 f!: Immediately before the grounded current limiting resistor {91 emits the laser, it is ungrounded and the 10th second capacitor a1, (ID)
The battery is charged at a ratio of k-1):1, and a bias voltage is applied to the PDaS. As the charging of the 10th second capacitor αOaD progresses and the bias voltage becomes higher, the sensitivity of the APD (19) increases. ) When a slightly higher voltage is reached, the AP
Da5 causes a breakdown phenomenon and generates micronoise. Then. This micronoise is detected by the breakdown detection circuit an, and the timing signal output from this circuit grounds the current limiting resistor {9} and the second capacitor aD, so that the APD a
The voltage applied to 9 drops by l/k times, and the ratio of this voltage drop is the ratio of the difference between the bias voltage that causes the breakdown phenomenon (hereinafter this voltage is referred to as the breakdown voltage) and the optimal bias voltage. If the value of constant k is selected so that fkb and diode α4 serve to prevent current from flowing out of the first capacitor atr and lowering the APD bias voltage when the current limiting resistor (9) is grounded.

In this way, the photodetector section <<5>> detects the breakdown voltage using the micronoise generated by the APD itself. moreover. By lowering the bias voltage at a constant rate from this value, the bias voltage is set to a value approximately equal to the optimal bias voltage. APD a! i can operate in an almost optimal sensitivity state. [Problem to be solved by the invention] In the above-mentioned photodetector section, the APD bias voltage can be optimized by lowering the voltage from the breakdown voltage at a constant ratio. I am trying to set the bias voltage. The ratio of the voltage difference between the breakdown voltage and the optimal bias voltage to the breakdown voltage (hereinafter this ratio will be referred to as 'f:I & appropriate drop voltage ratio) changes depending on the temperature, so it is necessary to maintain the voltage at a constant ratio like this. With the lowering method, the APD voltage may not be set in a manner that fully corresponds to the surrounding tolerance. For that purpose, APD
There was a problem that the sensitivity could not be brought out sufficiently.

This invention solves the above problem by changing the ratio of the voltage at which the APD bias voltage is lowered from the breakdown voltage depending on the ambient temperature. The purpose is to always be able to draw out the full sensitivity of the APD without being affected by the ambient temperature, and to prevent the ranging ability from being affected by temperature.

[Means to solve the problem]

This invention uses a capacitor whose capacitance changes depending on the ambient temperature instead of the conventional charging capacitor of the photodetector. The main voltage of the above capacitor is divided according to the ambient temperature. This divided voltage is applied to the APD when the APD 7' leakdown phenomenon occurs, so that the ratio of the voltage dropped from the breakdown voltage of the APD bias voltage changes depending on the surrounding temperature. It is.

[Effect]

In this invention, a capacitor whose capacitance value changes depending on temperature. AP is connected by FET etc. which acts as a switch.
Since the ratio of the voltage dropped from the breakdown voltage of the D bias voltage is set to change depending on the surrounding temperature, the APD always operates optimally depending on the surrounding temperature. The ranging ability can also be made unaffected by temperature.

〔Example〕

FIG. 1 is a structural diagram showing an embodiment of this invention, and F
+). The capacitors a0 to a are the same as the conventional capacitors.68a$ are capacitors with positive temperature capacitance change characteristics and O.

In this structure, the capacitor +1)1 having a positive temperature capacitance change characteristic operates in the same way as a conventional photodetector, except that the capacitance value increases in proportion to the surrounding temperature. A bias voltage is applied to the APDC 19 immediately before laser distance measurement begins. When the bias voltage becomes high and APDα9 causes a breakdown phenomenon. Breakdown detection circuit wholesale timing signal and the above 20th FETQ3 and diode α◆
Therefore, each of the above temperature capacitance change characteristics is positive. 0 capacitor α sand. The charge to the battery is stopped to prevent the APD bias voltage from exceeding the breakdown voltage.

It has been found through experiments that there is a correlation between the optimum voltage drop ratio and temperature, and the lower the temperature, the larger the optimum voltage drop ratio becomes. FIG. 5 shows this situation, and shows a characteristic that has a negative slope downward to the right with respect to temperature T.

Therefore, the ratio of voltage drop was made to match the characteristics shown in Figure 5. By controlling the bias so that the voltage is lowered from the breakdown voltage, it is possible to perform an optimal bias setting that matches the ambient temperature. The temperature capacitance change characteristics are positive. O capacitor α-. a9 and first FET
(I3 is for performing a voltage drop operation for this purpose. Among these, the capacitor αa. The charging voltage is divided according to the ambient temperature.If the capacitance values of the above capacitors as and as are respectively C1 (T) and C2 (where T is the ambient temperature), it is a capacitor with positive temperature capacitance change characteristics. In particular, capacitors aS with applied voltage and temperature capacitance change characteristics of O
The ratio to the voltage applied to C2 is C2:CI(T).

Therefore, if the capacitor AS with a temperature capacitance change characteristic of 00 is grounded with a FET that serves as a switch, the charging voltage will drop by the voltage applied to the capacitor α6, which has a positive temperature characteristic. The decreasing ratio 2 takes a larger value as the temperature becomes lower, as shown in equation (2).

C2 2=...
・・・・・・・・・-(421CI(T)+02 However, when TI<T2, C1(T1)<01(T2) The above first FEll3 is for causing this voltage drop.Switch operation The output side of the FET that performs the control operation is connected to the capacitor having a positive temperature capacitance change characteristic.The input side of the FET that performs the control operation is connected to the output terminal of the breakdown detection circuit an.

Therefore, the above hPDa5 causes a breakdown phenomenon.
During this period, the output of the breakdown detection circuit a is at logic level LOW, and this timing signal causes the charging voltage stored in the capacitor (II, a9) to be directly applied to APDfi!9, but APDa5 is not affected by the breakdown phenomenon. After the above timing signal is
This signal, which goes high, turns on the first FETea. As a result, the capacitor aS having a positive temperature capacitance change characteristic is grounded (a charging voltage dropped by the ratio 2 shown in equation 21 is applied to the APD u).

Therefore, in order to match the above voltage drop ratio z with the characteristics shown in Fig. 5, a capacitor α whose temperature capacitance change characteristics are positive and 0, respectively, is used.
By selecting the capacitance values of I1 and Q9 and the temperature capacitance change coefficient, the ratio of the voltage that lowers the APD bias voltage from the breakdown voltage can be matched with the optimal drop voltage ratio, so the APD bias voltage can be adjusted approximately according to the ambient temperature. It can be set in ideal conditions.

Figure 6. Figure 1. Figure 8. Figure 9 shows this situation. Charging voltage and divided voltage of the capacitor, respectively. Increase#
Output of A device atS. The output of the breakdown detection circuit α and the output of the APD bias voltage are shown along the time axis.

In the figure to FiAPD Q! 1 indicates the time when the breakdown phenomenon occurred and micronoise was generated. b.
Figure 6. Figure 9: 'r=T1, T=T
The second curve is the divided voltage. ^PD This shows how the bias voltage changes depending on the ambient temperature T.

From these figures, it can be seen that the charging voltage of capacitors α● and as is divided and generated according to the ambient temperature, and the instantaneous amplifier 6.1 and breakdown detection circuit an, in which APDa1 causes a breakdown phenomenon, detects micronoise. This causes a timing signal to be generated, and this timing signal stops the charging voltage from rising and at the same time only the divided voltage is applied to the APD. In other words. ratio 2
It can be seen that the voltage drop from the breakdown voltage of the APD bias voltage is also set in accordance with the ambient temperature since the voltage dropped by the voltage is applied to the APD.

In the end, the photodetector section configured in this way includes a current limiting resistor C9}, a second FET (13), a capacitor αa, α9, and a diode a whose temperature capacitance change characteristics are positive, respectively.
4. The charging voltage, which gradually increases due to the power of APD+13, amplifier αe, and breakdown detection circuit a, is connected to the two capacitors. It generates electricity by changing the voltage distribution depending on the surrounding temperature. Initially, the above charging voltage is above A
Joins PDα9 directly b. This increase in voltage causes the AP
D (Based on the micro-noise generated by 15 itself, the increase in APD bias voltage is stopped at the level of breakdown voltage. At the same time, the temperature capacitance is changed by the first FE'l3 based on the time information when the breakdown phenomenon occurs.) A capacitor AL with positive characteristics is grounded, and the charging voltage is AP, which is reduced by the voltage sensed by this capacitor.
In addition to D(151), an optimal bias voltage is set by dropping the voltage according to the ambient temperature.

Therefore, the APDα can always be operated in ideal conditions relative to the surrounding temperature. Therefore. It is possible to prevent the ranging ability from being affected by the ambient temperature.

1. In the above embodiment, a capacitor having a positive temperature capacitance change characteristic was used to divide the charging voltage according to the surrounding temperature. A capacitor with negative temperature capacitance change characteristics may also be used. Figure 2 shows one example of this. Use a negative capacitor ■ instead of a capacitor with temperature capacitance change characteristics of 00. Further, this embodiment is the same as the above embodiment except that a capacitor 89 having a temperature capacitance change characteristic of 0 is used instead of a capacitor having a positive temperature capacitance change characteristic. In this case, conversely, the capacitor whose temperature capacitance change characteristic is 0 is grounded by the first FET Q3 and a voltage drop occurs, so that the temperature capacitance change characteristic is 0. Negative capacitor α9. Each even capacitance value is C
2# Cs (T) (where T is the ambient temperature), the ratio W of voltage drop at this time is expressed by equation 31. 《
Similar to Equation 21, the lower the temperature, the larger the value, so the APD bias voltage can be set in a nearly ideal state according to the ambient temperature, similarly to the above embodiment.

However, when T1 < T2, Cx(T1) > C3(
T2) Furthermore. Capacitors having positive and negative temperature capacitance change characteristics may be used at the same time to divide the charging voltage according to the ambient temperature. FIG. 3 shows this implementation fIl for capacitors ■ with negative and positive temperature capacitance change characteristics, respectively. Using αS. This embodiment is the same as the above embodiment except that the capacitor ciD having a negative temperature capacitance change characteristic is grounded through the first FET Q3. The above temperature capacitance change characteristics are negative. Positive capacitor ω. The capacitance value of α● is c5
('r). Assuming C1(T) (where T is the ambient temperature), the voltage drop ratio Y in this case is shown by equation (4). Similar to equation 2), the lower the temperature, the larger the value. In addition to being able to set the APD voltage in an almost ideal condition according to the ambient temperature. Positive temperature capacity change characteristics. Since two types of negative capacitors are used in combination, there is an advantage that the number of series of temperature capacitance changes required to match the ideal characteristics can be as small as in the case of one type.

However, when TI<T2, C1(Tt)<CI
(T2) Cs (T1) > Cx (T2) In addition, an adjustment capacitor is connected in parallel with a capacitor that has a temperature change characteristic that plays the role of varying the voltage division ratio of the electric voltage depending on the temperature. may be connected to. ia
Figure 4 shows an example of this.6, am, (1
) have positive temperature capacitance change characteristics. Negative capacitor.
l2I+ is a vI4 adjustment capacitor, and the rest is the same as in the above embodiment. Features of the above capacitors. (a) If the capacitance values of an are CI (T), CM (T), and C4, respectively, the ratio of voltage drop in this case is shown by the formula Further, the voltage drop characteristics with respect to temperature can be adjusted by the capacitance value C4 of the adjustment capacitor I2n. Therefore, in this case, there is an advantage that the APD bias voltage can be set to a more ideal state depending on the ambient temperature.

However, when TI<T2, C1(Tt)<CI
(T2) Cg(Tt)>Cs(Tz) [Effects of the Invention] The present invention detects the breakdown voltage of the APD by using the conventional photodetecting section described above using the micronoise generated by the APD itself. The APD bias setting was performed by dropping the voltage at a fixed ratio from this breakdown voltage, but now the optimal bias voltage is determined by changing the voltage drop ratio depending on the ambient temperature. The APD bias is set according to the ambient temperature. Therefore, the light detection ability of the APD can always be brought out at its highest level. Therefore, distance measurement is not affected by ambient temperature. Always. can be done at its best.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram showing one embodiment of the present invention, Figs. 2 to 4 are diagrams showing other embodiments of the invention, and Fig. 5 is a diagram showing the relationship between the optimum voltage drop ratio output and temperature. , Fig. 6. Figure 1. Figure 8. Figure 9 shows the charging voltage of the capacitor and the output of amplifier ae, respectively. Output of breakdown detection circuit a,
A diagram showing the APD bias voltage along with the time axis. 1st
Figure 0 shows the configuration of the distance measuring device. Figure 1) is a diagram showing the configuration of a conventional photodetector. In the figure (1) is the laser oscillator. 121ti transmission optical system.
(31 is the receiving optical system. {4} is the detector, (5) is the photodetector. (6) is the high voltage circuit. (7) is the counting circuit, (8) is the power supply. 《91 is the current limiting resistor. .αo, an is the 10th
Second capacitor. α2, a3 are the 10th second FET,
α4 is a diode. α9 is APD, a● is amplifier,
+171 is a breakdown detection circuit, am, as,
CB has positive temperature capacitance change characteristics. 0. Negative capacitor. Qn is an adjustment capacitor. In the figure. Identical or equivalent parts are designated by the same reference numerals.

Claims (4)

[Claims] (1) A high-voltage circuit that generates high voltage, a current-limiting resistor that limits the current flowing out from the high-voltage circuit, and a function that gradually increases the voltage by accumulating the current flowing through the current-limiting resistor. Temperature capacity change characteristics are 0,
The first and second capacitors connected in positive series and the first to short-circuit the terminals of the second of the first and second capacitors to discharge the voltage accumulated in this capacitor. FET, and a second FE that serves to connect or disconnect high voltage to the first and second capacitors.
T, a diode that prevents current from flowing out of the capacitor when the high voltage is cut off, and an APD (Ava- lunchPhoto
Diode), an amplifier that performs amplification to capture the micronoise that occurs during the breakdown phenomenon that occurs when a bias voltage slightly higher than the APD bias voltage that exhibits the highest sensitivity is applied to the APD, and the APD that uses the micronoise to has a breakdown detection circuit that detects a bias voltage that causes a breakdown phenomenon as timing information, and initially the charging voltage stored in the first and second capacitors is directly applied to the APD, As the voltage increases, the APD causes a breakdown phenomenon, and at the same time, the charging of the first and second capacitors is interrupted by the timing signal of the breakdown detection circuit and the second FET.
The increase in the PD bias voltage is stopped, and the timing signal, the first and second capacitors, and the first
The charging voltage is divided by the FET, and the voltage applied to the APD is controlled by utilizing the fact that the capacitance change caused by the positive series temperature capacitance change characteristic of the second capacitor appears as a change in the voltage division ratio of the charging voltage. 1. A distance measuring device comprising: a photodetecting section that causes the APD to operate optimally depending on the ambient temperature by decreasing the amount of light depending on the ambient temperature. (2) A high-voltage circuit that generates high voltage, a current-limiting resistor that limits the current flowing out from the high-voltage circuit, and a function that gradually increases the voltage by accumulating the current flowing through the current-limiting resistor. Temperature capacitance change characteristics are negative,
A first FET that discharges the voltage accumulated in this capacitor by shorting between the terminals of the second capacitor and the second capacitor of the first and second capacitors connected in series; and a second FE that serves to connect or disconnect high voltage to the first and second capacitors.
T, a diode that prevents current from flowing out of the capacitor when the high voltage is cut off, and an APD (Avalan-che Ploto Di) that performs optical amplification using the charged voltage stored in the first and second capacitors as a bias source.
ode), an amplifier that performs amplification to capture the micronoise that occurs during the breakdown phenomenon that occurs when a bias voltage slightly higher than the APD bias voltage that exhibits the highest sensitivity is applied to the APD, and the APD has a breakdown detection circuit that detects a bias voltage that causes a breakdown phenomenon as timing information, and initially the charging voltage stored in the first and second capacitors is directly applied to the APD, As the voltage increases, the APD causes a breakdown phenomenon, and at the same time, the charging of the first and second capacitors is interrupted by the timing signal of the breakdown detection circuit and the second FET.
The increase in the PD bias voltage is stopped, and the timing signal, the first and second capacitors, and the first
The charging voltage is divided by the FET, and at this time, the first
The capacitance change caused by the temperature capacitance change characteristic of the negative series of the capacitor appears as a partial pressure change of the charging voltage. 1. A distance measuring device characterized by comprising a photodetecting section that operates optimally depending on the temperature of the device. (3) A high-voltage circuit that generates a high voltage, a current-limiting resistor that limits the current flowing out of the high-voltage circuit, and a function that gradually increases the voltage by accumulating the current flowing through the current-limiting resistor. Temperature capacitance change characteristics are negative,
A first FET that shorts the terminals of the tenth positive series-connected second capacitor and the second capacitor of the first and second capacitors to discharge the voltage accumulated in this capacitor. and a second FE that serves to connect or disconnect high voltage to the first and second capacitors.
T, a diode that prevents current from flowing out of the capacitor when the high voltage is cut off, and an APD (Avala-D) that performs optical amplification using the charging voltage stored in the first and second capacitors as a bias source. nchePloto
Diode), an amplifier that performs amplification to capture the micro-noise that occurs during the breakdown phenomenon that occurs when a bias voltage slightly higher than the APD bias voltage that exhibits the highest sensitivity is applied to the APD, and an amplifier that performs amplification to capture the micro-noise that occurs when the APD is A breakdown detection circuit detects a bias voltage that causes a breakdown phenomenon as timing information, and initially the charging voltage stored in the first and second capacitors is directly applied to the APD, and the When the APD causes a breakdown phenomenon as the voltage increases, the charging of the first and second capacitors is interrupted by the timing signal of the breakdown detection circuit and the second FET to increase the APD bias voltage. The charging voltage is stopped from rising, and the charging voltage is divided by the timing signal, the first and second capacitors, and the first FET, and at this time, the first
, the voltage applied to the APD is lowered according to the surrounding temperature by utilizing the fact that the capacitance changes caused by the temperature capacitance change characteristics of the negative series and positive series of the second capacitor appear as changes in the partial pressure of the charging voltage. By letting APD
1. A distance measuring device characterized by comprising a light detection section that operates optimally depending on the surrounding temperature. (4) The distance measuring device according to claim 1, 2 or 3, characterized in that a capacitor for adjusting voltage drop characteristics with respect to temperature is connected in parallel with the first and second capacitors connected in series.